Ralackk: Check your start menu, gog.com folder for the Gabriel knight 3 game, if there are any graphical setting options outside of the game they should be accessable there. Make sure to right click and run them as administrator though to keep the settings.

cducharme: Thanks, I did check that and there is just an option to uninstall. Nothing in the gog directory either that looks like a setup program...

Ralackk: Hmm in that case did you check the games folder for any .conf files or anything of that sort that you could edit settings manually?
Also are you 100% sure you have changed nothing sinse last time you played? No new graphics driver installs or changing a setting in your graphics card control panel to make a different game run properly that you forgot to change back?

Collector: The settings for GK3 are stored in the registry.
HKEY_CURRENT_USER\Software\Sierra On-Line\Gabriel Knight 3
You could delete this key and it would be like the very first time that you ran the game, but still have your save games. Just remember to be careful when making any changes to the registry.

Patryn: All right, my idea worked!
It truly was just the SIERRA.AVI file that was causing the lock up and blank screen.
As I didn't want to install some converter-software, I went to the online converter at http://www.mediaconverter.org/ and uploaded my SIERRA.AVI (from the DATA subfolder) and converted it into an AVI.
Yeah, it sounds like the same but the site uses some other codec which actually makes the avi rather ugly looking - but only takes up about 10% of it's original size. And, really, it's just a 16 second clip of the sierra logo flying in.
Anyway it seems - so far - that SIERRA.AVI is the only file causing the lock up as I left all the other files untouched. Most of the other video files are BIK-files anyway.
Well, the game works now and I hope this will work for you as well.
Supplemental: It appears that there are a few very small AVI-clips that sue the same codec. They are just displaying some lines. If I remember correctly, these could be the ones displayed on the laptop when Grace analyzes "Le Serpent Rouge" later in the game. I'll recode these AVIs as well - if the game crashes later in the game when I start analyzing, I'll now that this is the cause.

Patryn: I think the message indicates that your desktop has to be set to 16 bit mode for GK3 to run in a window. Apparently, the engine is not able to set itself to 16 bit if it is not running fullscreen.
I downloaded GK3 as well and I have the same problem. After some testing I think it's because of the Sierra-logo-movie.
I tried to play it and Windows Media Player cannot play it and crashes. KMplayer - which doesn't use Windows codecs - is able to play it.
This is strange as the AVI file uses a simple Cinepak-codec which is usually preinstalled and came with every Windows version from 95 onward.
Perhaps my XP uses a newer version which doesn't work and crashes not only Media Player but the game as well.
My next step would be to convert SIERRA.AVI to some other codec that Media Player is able to play. But right now I don't have the time to try this.
Maybe tomorrow.

Patryn: All right, my idea worked!
It truly was just the SIERRA.AVI file that was causing the lock up and blank screen.
As I didn't want to install some converter-software, I went to the online converter at http://www.mediaconverter.org/ and uploaded my SIERRA.AVI (from the DATA subfolder) and converted it into an AVI.
Yeah, it sounds like the same but the site uses some other codec which actually makes the avi rather ugly looking - but only takes up about 10% of it's original size. And, really, it's just a 16 second clip of the sierra logo flying in.
Anyway it seems - so far - that SIERRA.AVI is the only file causing the lock up as I left all the other files untouched. Most of the other video files are BIK-files anyway.
Well, the game works now and I hope this will work for you as well.
Supplemental: It appears that there are a few very small AVI-clips that sue the same codec. They are just displaying some lines. If I remember correctly, these could be the ones displayed on the laptop when Grace analyzes "Le Serpent Rouge" later in the game. I'll recode these AVIs as well - if the game crashes later in the game when I start analyzing, I'll now that this is the cause.

Collector: A lot of times when installing newer codecs they will disable or uninstall other ones already on the system and codecs can be installed as part of the install of other programs/games without you even knowing about it.

cducharme: Well, I've come back to try to fix this issue again. I've done all sorts of things like trying to use another .avi file so that the game loads some video file that does work before the game starts, but for whatever reason, that don't work either. It's frustrating because the game used to work. Does anyone have the 'generic' driver that gk3 uses to play its video files? Perhaps as was suggested below some subsequent install 'upgraded' my driver for playing ancient video files... I'm not even sure what I'm asking for, because I'm not sure what 'type' of video file it is. In any case, if someone has a working Gk3, and knows what driver it utilizes, perhaps I could have it?

Thanks for all the good help here. cducharme: Well... I *swear* I tried this earlier... but apparently just removing the sierra.avi file from the folder altogether will skip the sierra logo video and let you play. I'm totally confused. Can't imagine why I wouldn't have tried this earlier. Oh well, those of you crashing out, try just moving out the sierra.avi file.

-Cam